The objective of this proposal is to obtain continuing support for the program-project grant that has been concerned for the past 17 years with the study of the dynamic state of body constituents in man and experimental animals. The program is multidisciplinary, involving physicians, physicists, chemists, engineers and computer experts; and multidepartmental, involving departments of both the Schools of Medicine and Hygiene and Public Health of the Johns Hopkins Medical Institutions, the Graduate Chemistry Division of Johns Hopkins University and the Applied Physics Laboratory of the Johns Hopkins University. The program supports a nucleus of investigators in a broad, continuing program oriented toward obtaining new knowledge about the dynamic state of body constituents by the application of a variety of new radioactive tracer techniques that we will design, develop, and evaluate. These studies include but are not limited to the following scientific objectives: 1) development and assessment of improved methods for the quantitative measurement of physiologic processes in various regions of the body, 2) elucidation of the general principles governing the distribution of radiolabeled elements, compounds and cells within the body, and 3) application of our advances of knowledge and methodology to medical diagnosis and the solution of selected biomedical problems. The program involves both basic science and clinical departments of these school's and has a well-equipped core research facility sufficiently versatile to permit a broad approach to the solution of important biomedical problems. The program has achieved considerable success in the past, the current projects seem to offer great promise, and the proposed program promises to produce results of importance both to fundamental knowledge and applied medical research.